1. Field of the Invention
This invention relates generally to the storage of information on hard disk drives and more particularly to a method for optimizing the storage capacity of miniature disk drives.
2. Description of the Prior Art
In miniature disk drives, the transducers are preferably loaded into, and unloaded from flight above the surface of the spinning magnetic storage media, as opposed to utilizing take-off from and landing on the magnetic storage media. Loading and unloading of the transducers above, as opposed to on, the storage media is referred to as dynamic head loading.
For a more detailed discussion of dynamic head loading, see U.S. Patent application Ser. No. 07/766,479, entitled "Rigid Disk Drive with Dynamic Head Loading Apparatus" of James H. Morehouse et al., which issued as U.S. Pat. No. 5,237,472 on Aug. 17, 1993, and U.S. patent application Ser. No. 07/629,957, entitled "Rigid Disk Drive with Dynamic Head Loading Apparatus" of James H Morehouse et al. which issued as U.S. Pat. No. 5,289,325 on Feb. 22, 1994, both of which are incorporated herein by reference in their entirety. See also, U.S. Pat. No. 4,933,785, entitled "Disk Drive Apparatus Using Dynamic Loading/Unloading" which issued to Morehouse et al., on Jun. 12, 1990 and U.S. Pat. No. 5,027,241, entitled "Data Head Load Beam for Height Compacted, Lower Power Fixed Head and Disk Assembly" which issued to Hatch et al. on Jun. 25, 1991.
In the various different embodiments of dynamic head loading, a transducer 11 (FIG. 1), alternatively referred to as the read/write head, magnetic head, or slider, is affixed to a load beam 10 which in turn is affixed to a rotary actuator 6. The accuracy with which the structure is made is limited by mechanical manufacturing tolerance.
The load beam-transducer assembly is moved into contact with or from a stationery loading ramp 15 to dynamically load or unload, respectively, the load beam-transducer assembly. Stationery loading ramp 15 typically encroaches over the outer diameter of storage media 2, i.e., a disk or disks.
When transducer 11 is unloaded from stationery loading ramp 15, prerecorded servo patterns on disk 2 are used to accurately locate information in a particular track or tracks on disk 2. The prerecorded servo patterns are written on a disk using a servo track writer (STW), that can precisely position transducer 11. However, as the capacity of miniature disk drives is increased and as disk drives are made smaller while maintaining the same storage capacity, there is a need for even more precise positioning of the servo patterns so that the number of tracks on each surface of the disk can be optimized.
In disk drives that utilize dynamic head loading, stationery loading ramp 15 in combination with the mechanical manufacturing tolerances and disk runout limit the accuracy of the servo track writer. Specifically, as the servo track writer positions transducer 11 near the outer diameter of disk 2, transducer 11 may encounter interference from stationery loading ramp 15. Therefore, to the extent that stationery loading ramp 15 encroaches over the outer diameter of disk 2, the usable disk area, and consequently the available recording area, is reduced.
The problem associated with stationery loading ramp 15 is further exacerbated by the mechanical manufacturing tolerances associated with the positioning of stationery loading ramp 15 relative to the outer diameter of disk 2, and the positioning of the magnetic heads, e.g., transducer 11, on the load beams relative to stationery loading ramp 15. For disk drives with multiple magnetic heads, the variation in the various magnetic heads' position relative to stationery loading ramp 15 creates a high probability that at least one magnetic head encounters interference from stationery loading ramp 15 as the servo track writer writes the tracks on the outer diameter of the disk.
If a magnetic head 11 (FIG. 1) encounters interference from stationery loading ramp 15, i.e., ramp 15 starts to unload magnetic head 11, the servo field information is not completely written at the proper location on disk 2 by the servo track writer. Consequently, to assure that each track was properly written, the servo track writer was programmed to compensate for the mechanical manufacturing tolerances. Specifically, a reference track, which is commonly referred to as track zero, was written a predetermined distance from the outer disk diameter. The predetermined distance was calculated using worst case mechanical tolerances. Subsequently, the servo track writer moved radially in from track zero and sequentially formatted each track with the servo field information.
Placement of track zero based on the worst case mechanical manufacturing tolerances leaves usable disk space unutilized and so the effective data storage capacity of the disk drive is reduced. Alternatively, track zero can be moved closer to the outer diameter. Moving track zero closer to the outer diameter increases the effective data storage capacity, but only at the expense of decreased reliability and yields. Therefore, a method is needed that increases the effective data storage without decreasing reliability and yields.